1. Field of the Invention
This application claims the benefit of Japanese Patent Application No. 2005-374093, filed Dec. 27, 2005, which is incorporated herein by reference.
The present invention relates to image reading devices that are used in multifunction devices (“MFDs”), and more specifically relates to the structures of the image sensor units used in these image reading devices.
2. Description of Related Art
FIG. 1 is a perspective view of significant elements of a known conventional image reading device. This image reading device has an image sensor unit 10. Image sensor unit 10 has a contact-type image sensor (“CIS”) 11 and a carriage 12 that holds contact image sensor 11. Carriage 12 is supported by a guide shaft 13 and slides in the direction indicated by arrow 14 by means of a slide device not shown in the drawings. Carriage 12 has a pair of bearings 15, 16, and guide shaft 13 is inserted or extends through bearings 15, 16. In addition, a contact glass plate that is not shown in FIG. 1 is disposed above image sensor unit 10, and a document is placed on this contact glass plate for image reading. Contact image sensor 11 reads an image from the document when carriage 12 slides in the direction indicated by arrow 14.
In order to achieve higher-precision image reading, carriage 12 must not chatter with respect to guide shaft 13 during sliding. If carriage 12 chatters against guide shaft 13, contact image sensor 11 oscillates or vibrates in the direction of arrow 17 during image reading, preventing the image from being read properly. For this reason, bearings 15 and 16 in known image reading devices have mechanisms for tightening guide shaft 13 in the radial direction, such as in Japanese Unexamined Patent Application Publication No. 2003-158614. Further, members have been provided for filling in gaps between bearings 15, 16 and guide shaft 13, such as in Japanese Unexamined Patent Application Publication No. H05-145705.
Nevertheless, a distance 18 between the pair of bearings 15, 16 is extremely small relative to the dimension in the length-wise direction of carriage 12. For this reason, dramatic effects have not been attained, even though these known-types of countermeasures have been employed. In addition, distance 18 may be increased in order to prevent chattering of carriage 12 against guide shaft 13. Nevertheless, when distance 18 is increased, the external dimension of the image reading device in the direction of arrow 14 also is increased. There is a strong incentive for reducing the size and weight of image reading devices that employ contact image sensors, and increasing distance 18 runs counter to this demand.